Question

Oscar has an old-fashioned lantern projector that uses a candle and a lens to project a slide onto the wall. The lens is 1.3 cm from the slide and projects an image onto a screen 80 cm away. Oscar adds a lens to the original lens to allow him to project an image onto a screen 30 cm away.

1. What is the power of the original lens?

2. What is the desired power of the combined lenses?

3. What power lens must Oscar add?

Answer 1

solution Given Lens 1.3cm, away 80cm - oscal adds lens on screen away 30cm a, To find powel of original ung U:-1.3 cm V-80 cm a sign indicates distance is opposite direction $ +$ +3to tits Ś - 1:84780 = 81.3 Falloum cm Power = 100 - 100 - =78-170 ... Powel of original lens /P = 78.17D] - To find desired powel of combined lenses 4= 4.3 VE 30cm • -*-* = to take this 104 81.3 104/81:3 $ = 13.420 = 3,3 F .com 100 100 80.25 D 39131.3 i. Powel of Desired lenses IP = 80.25D

c. To tind what powee lens must oslog add F F F2 104 81.3 81.3 104 fi = lou com F2 = ? 34121.3. - 1041 813 + Fz 3.3 - 2014 39 - 3255.2-3170.7 = 84.5 4056. F2=48 D Pa = 100 = 60 - 2.08 D .: Regeired power P2 = 2.08D 4056 100 - 2.0 X